A nanocomposite permanent magnet, including a hard magnetic phase such as an Nd2Fe14B phase with a very small size of a nanometer scale and soft magnetic phases such as α-Fe in the same metal structure (which will be referred to herein as a “nanocomposite magnet”), is currently under development. In a nanocomposite magnet, crystal grains are magnetically coupled together via exchange interactions and therefore, the nanocomposite magnet has excellent performance.
In the field of electronic products including small-sized motors and sensors, magnets with high remanence are in high demand. To increase the remanence of a nanocomposite magnet to meet this demand, it is effective to increase the percentage of the α-Fe phase to the overall nanocomposite magnet. This is because since the saturation magnetization of the α-Fe phase is higher than that of the Nd2Fe14B phase or that of the Fe—B phase, the increase in the percentage of the α-Fe phase to the nanocomposite magnet means that the overall magnet will have increased remanence.
Patent Documents Nos. 1 and 2 disclose α-Fe based nanocomposite magnets. In these nanocomposite magnets, most of their soft magnetic phases is α-Fe. That is why these nanocomposite magnets are expected to achieve a high remanence of 0.9 T or more. However, the conventional α-Fe based nanocomposite magnets have a coercivity of 400 kA/m or less, which is too low to use them in actual products.
The applicant of the present application developed an α-Fe based nanocomposite magnet, in which α-Fe phases with a significantly decreased size are distributed on the grain boundary of Nd2Fe14B crystal grains by suppressing the nucleation and growth of the α-Fe phases with Ti added, and disclosed such a magnet in Patent Documents Nos. 3 and 4. That nanocomposite magnet has as high a remanence Br as 0.9 T or more and a coercivity HcJ of more than 400 kA/m, and can be used effectively to make a bonded magnet. And those patent documents say that the bonded magnet also has as high a remanence Br as 0.6 T or more. The applicant of the present application further disclosed a bulk magnet of a Ti-including nanocomposite magnet in Patent Document No. 5.